ntdll: Perform the offset checks also for a serial device.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://newtestbot.winehq.org/JobDetails.pl?Key=2267

Your paranoid android.


=== w7pro64 (32 bit comm) ===
comm.c:863: Test failed: WaitCommEvent failed with a timeout
comm.c:875: recovering after WAIT_TIMEOUT...
comm.c:886: Test failed: WaitCommEvent error 0
comm.c:888: Test failed: WaitCommEvent: expected EV_TXEMPTY, got 0
comm.c:892: WaitCommEvent for EV_TXEMPTY took 1014 ms (timeout 1000)
comm.c:894: Test failed: WaitCommEvent used 1014 ms for waiting
comm.c:1561: test_AbortWaitCts timeout 500 handle 000000F8
comm.c:1528:  Changing CommMask on the fly for handle 000000F8 after timeout 500